MOUNTING
BRACKET
SCREW 4
R
EQUIRED
F
ig. 3
Fig. 4
Fig. 5
F
ig. 6
F
ig. 7
F
ig. 5B
Fig. 6B
S
urface Mounting: Drill appropriate holes in panel, using the dimensions shown
i
n Fig. 2. Hold the flowmeter in position in front of the panel and install the clamp
bolts from the rear. (The mounting clamps may be used as washers, if desired, by
installing them backwards or straightening them out.) Pipe up inlet and discharge
following the directions in the previous sections.
S
urface Mounting on Piping Only: An alternate method of surface mounting,
o
mitting the clamp bolts and supporting the flowmeter solely on the connecting pip-
ing, is possible. For this method, extra-long or straight pipe threads should be used
so that nuts may be run onto the pipe and later tightened against the back of the
panel to retain the unit in proper position. Use appropriate hole layout in formation
from Fig. 2, but omit the small holes.
Surface Mounting on Piping Only Without Panel: For a temporary or laboratory
type installation, the panel may be omitted altogether and the flowmeter installed
d
irectly in rigid piping. Its light weight permits this without difficulty.
O
PERATION
To start system, open valve slowly to avoid possible damage. Control valves on BV
and SSV models are turned clockwise to reduce flow, counter-clockwise to
increase flow (valve is designed for flow adjustment only, not intended to be used
as an open/shut-off valve). A nylon insert is provided in the threaded section of the
valve stem to give a firm touch to valve and to prevent change of setting due to
vibration.
The performance of low range units used in air or gas applications may be affect-
ed by static electricity. Excessive static charge may cause the ball float to behave
erratically or provide a false reading. To ensure the proper function of the unit, the
application should be designed to minimize or dispel static electricity.
The standard technique for reading a Variable Area Flowmeter is to locate the high-
est point of greatest diameter on the float, and then align that with the theoretical
center of the scale graduation. In the event that the float is not aligned with a grad,
an extrapolation of the float location must be made by the operator as to its loca-
tion between the two closest grads. The following are some sample floats shown
with reference to the proper location to read the float.
Variable Area Flowmeters used for gases are typically labeled with the prefix “S” or
“N”, which represents “Standard” for English units or “Normal” for metric units. Use
of this prefix designates that the flowmeter is calibrated to operate at a specific set
of conditions, and deviation from those standard conditions will require correction
for the calibration to be valid. In practice, the reading taken from the flowmeter
scale must be corrected back to standard conditions to be used with the scale
units. The correct location to measure the actual pressure and temperature is at the
exit of the flowmeter, except when using the Top Mounted Valve under vacuum
applications, where they should be measured at the flowmeter inlet. The equation
to correct for nonstandard operating conditions is as follows:
Q
2
= Q
1
x P
1
x T
2
P
2
x T
1
Where: Q
1
= Actual or Observed Flowmeter Reading
Q
2
= Standard Flow Corrected for Pressure and Temperature
P
1
=
Actual Pressure (14.7 psia + Gage Pressure)
P
2
=
Standard Pressure (14.7 psia, which is 0 psig)
T
1
= Actual Temperature (460 R + Temp °F)
T
2
= Standard Temperature (530 R, which is 70°F)
Example: A flowmeter with a scale of 10-100 SCFH Air. The float is sitting at the 60
g
rad on the flowmeter scale. Actual Pressure is measured at the exit of the meter
a
s 5 psig. Actual Temperature is measured at the exit of the meter as 85°F.
Q
2
= 60.0 x (14.7 + 5) x 530
14.7 x (460 + 85)
Q
2
= 68.5 SCFH Air
CAUTION: Do not completely unscrew valve stem unless the flowmeter is unpres-
surized and drained of any liquid. Removal while in service will allow gas or liquid
t
o flow out the front of the valve body and could result in serious personal injury.
F
or applications involving high pressure and/or toxic gases or fluids, please con-
t
act factory for details.
MAINTENANCE
The only maintenance normally required is occasional cleaning to assure reliable
operation and good float visibility.
Disassembly: The flowmeter can be disassembled for cleaning simply as follows:
1. Remove valve knob from RMB or RMC -BV or -SSV units by pulling the knob
forward. It is retained by spring pressure on the stem half-shaft so that a gentle pull
will remove it. On RMA-BV or -SSV models, turn the valve knob counter-clockwise
until the threads are disengaged. Then withdraw the stem from the valve by gently
pulling on the knob.
2. Remove the four mounting bracket screws located in the sides of the flowme-
ter. See Fig. 3. Pull the flowmeter body gently forward away from the back plate to
avoid undue strain on the body. Leave the piping connections intact. There is no
need to disturb them. See Fig. 4.
3. Threaded body style flowmeters - Remove the slip cap with a push on a screw-
driver as shown in Fig. 5. Remove the plug ball stop as shown in Fig. 6 using allen
wrench sizes as follows: Model RMA - 1/4˝, Model RMB - 1/2˝ and Model RMC -
3/4˝ Threadless body style flowmeters - Release the plastic retaining clip with a
screw driver (Figure 5B), it will unclip from the valve body (TMV Option) or the plug
ball stop, slide the clip back until the valve body or ball stop can be removed. The
clip will remain in the body for convenience. Using a screwdriver gently lift up on
the plug in the groove as shown in Figure 6B until the o-ring seal is released and
remove the plug. For the TMV option gently pull up on the valve knob to release
the valve body seals and remove the valve.
4. Take out the ball or float by inverting the body and allowing the float to fall into
your hand, as shown in Fig. 7. (Note: It is best to cover the discharge port to avoid
losing the float through that opening.)
Cleaning: The flow tube and flowmeter body can best be cleaned with a little pure
soap and water. Use of a bottle brush or other soft brush will aid the cleaning. Avoid
benzene, acetone, carbon tetrachloride, alkaline detergents, caustic soda, liquid
soaps (which may contain chlorinated solvents), etc. Also, avoid prolonged immer-
sion, which may harm or loosen the scale.
Reassembly: Simply reverse steps 1 through 4 and place the flowmeter back in
service. A little stopcock grease or petroleum jelly on the “O” rings will help main-
tain a good seal as well as facilitate assembly. No other special care is required.
DWYER INSTRUMENTS, INC.
Phone: 219/879-8000 www.dwyer-inst.com
P
.O.
BOX
373
•
MICHIGAN
CITY
,
IN
46360,
U.S.A.
Fax:
219/872-9057
e-mail:
[email protected]©Copyright 2015 Dwyer Instruments, Inc. Printed in U.S.A. 3/15 FR# 440197-00 Rev. 23
Teflon
®
is a registered Trademark of E.I. DuPont Company